1. Field of the Invention
This invention relates to a camera and, more particularly, to an improvement in a film transport device for maintaining the alignment of a film cartridge.
2. Description of the Prior Art
Recently, a type of camera has been proposed in U.S. Pat. No. 4,864,332 in which a film having a magnetic memory portion is used and information such as, a shutter speed, an aperture value, and a title are written on or read from this magnetic memory portion by a magnetic head.
Also, a pre-wind type of camera has been proposed and manufactured as an article of commerce in which the film is first wound around a spool and is then rewound into the film cartridge each time a frame is exposed. If the pre-wind type of camera is provided with a magnetic head and the film having a magnetic memory portion mentioned above, the following problem arises.
In order to write information on the magnetic memory portion of the film or reading out information therefrom, it is necessary to feed the film at a constant and a high speed.
The reason why feeding the film at a constant speed is necessary is because in a case where signals are read by the magnetic head as changes in the magnetism of the magnetic memory portion occur, the intervals of the signals are recognized as the content of information stored on the magnetic memory portion. Thus, a change in the film feed speed causes a change in the intervals of the signals, resulting in a detection failure.
The reason why feeding the film at a high speed is necessary is that unless the film is fed at a high speed, the magnetic flux will change so little so that the desired accuracy of the signals cannot be obtained.
Information may be written on or read from the magnetic memory portion of the film while the film is being rewound in the film cartridge. During this operation, if the film cartridge is inclined relative to the axis of a film rewinding fork, a shaft of the film cartridge and the film rewinding fork cannot be smoothly engaged and the load imposed on the film rewinding fork fluctuates. The film rewinding speed is thereby changed, resulting in an error in writing or reading information with the magnetic head.
This problem will be explained below with reference to FIGS. 7, 8 and 9. FIG. 7 is a longitudinal sectional view of a film cartridge chamber 111a in which a film cartridge 112 is accommodated in a camera body 111. Film cartridge 112 has a portion 112a for engagement with a fork portion 113a of a film rewinding fork 113 to which a fork drive gear 113b is connected.
Generally, the film cartridge size varies within the tolerance limit, and film cartridge chamber 111a has a size slightly larger than the film cartridge size so as to receive a film cartridge 112 in any shape. Ordinarily, for this reason, film cartridge 112 is set in film cartridge chamber 111a comparatively loosely so as to be off-centered relative to film cartridge chamber 111a at its one end while being engaged at the other end with the film rewinding fork portion 113a.
A spring member (not shown) or the like may therefore be used to press film cartridge 112 on the surfaces of portions 111b and 111c of the film cartridge 112, to prevent play between the film cartridge 112 and the camera body surfaces 111b and 111c, as shown in FIG. 8. However, as shown in FIG. 9, in the case of the ordinary film cartridge, the center defined by center lines 113C.sub.1 and 113C.sub.2 of the film rewinding fork, i.e., the axis of the film rewinding fork and the center defined by center lines 112C.sub.1 and 112C.sub.2 of the film cartridge, i.e., the axis of the film cartridge deviate from each other, since the axial center position of the film rewinding fork in the film cartridge chamber is determined so that a film cartridge having a maximum size can be suitably received as mentioned above. Therefore, the film rewinding fork cannot be driven smoothly and the film rewinding speed is changed.